A sea is commonly defined to be an extended body of saline water associated with one of the worlds five oceans (Atlantic, Indian, Pacific, Arctic, and Southern oceans). Some seas can appear to be distant from the ocean to which they are associated, like the Black Sea which is connected to the Atlantic Ocean, two thousand miles away, via the Mediterranean Sea and several very narrow straits.

Other bodies of inland waetr carry the name sea but are not directly associated with one of the world's oceans, such as the Caspian Sea and the Aral Sea. In most cases, seas are areas of an oceans that are close to and bounded to a greater or lesser degree by land.The degree to which seas are enclosed by land affects the degree to which they share water flows with the larger oceans or seas which they conect to. There are two types of sea defined by their degree of enclosure and connection to larger bodies of water:

Marginal seas are partially enclosed by land (e.g., a bay, a peninsula, islands). Because of their openness to the larger ocean or sea, marginal seas share the currents formed by ocean winds and these currents dominate water circulation. Marginal seas are far more common than mediterranean seas.Examples of marginal seas include (with dominating ocean or larger sea in parentheses): Barents Sea (Arctic); English Channel (Atlantic); Aegean Sea (Mediterranean); Red Sea (Indian); Coral Sea (Pacific); and the Scotia Sea (Southern)

Mediterranean seas are mostly enclosed by land and thereby have limited ability to share the currents of an adjoining ocean or larger sea. Water circulation in mediterranean seas is dominated by salinity and and temperature differences rather than winds. Examples of marginal seas include (with limited connectivity ocean or larger sea in parentheses): Mediterranean Sea (Atlantic); Arctic Mediterranean Sea (including the three "Nordic Seas" - Greenland Sea, Iceland Sea, and Norwegian Sea; and the Arctic Ocean).

Regional seas are bodies of water smaller than the main sections of the world ocean that is bound by geographic and/or hydrographic regions. Examples include the Adriatic Sea, Greenland Sea, Solomon Sea and Yellow Sea. Regional seas can be classifed further as marginal Seas or mediterranean seas.

Epeiric seas are associated with the marine transgressions of the geologic past, which are either attributed global eustatic sea level changes, local tectonic deformation, and are sometimes semi-cyclic. These seas can be warm or cold; several were extant toward the winding doewn of the most recent Ice Age, when sea level rose more rapidly than some areas could isostatically adjust. Present day examples are the Java Sea in Indonesia and the Persian Gulf

Since there no strict scientific definition of the term sea, it is not surprising that there is no single defined list of the seas of the world. Rather, there are bodies of water that are widely referred by a given term and are thereby listed here. Some might, with good reason, exclude some of the areas on this list and include others. Thus, the following list is not presented as exhaustive.